Biological component-measuring devices that have been used in the hospital are sometimes used continuously for a long time. Biological component-measuring devices used in this manner have problems, such as variation of measured values that increases with time, caused by deterioration. Devices, such as artificial endocrine pancreas devices, which carry out a closed loop control where components in the blood, a body fluid, of a patient, such as glucose, are measured continuously or at intervals, and liquid medicines such as insulin are injected into the patient based on the measurement in order to control the patient's conditions, require accurate and safe operation during their use, often over a long period of time. Specifically, it is said that an artificial endocrine pancreas device should be capable of providing accurate measurement for a period from about four hours to about one week.
When biological components such as glucose in a body fluid such as blood are measured, the body fluid withdrawn from a living organism is usually diluted with a diluent including a mixture of physiological saline and an anticoagulant, prior to the measurement. With artificial endocrine pancreas devices that are used for a long time, deterioration in device parts and abnormal blood withdrawal sometimes cause changes in dilution. These changes in the dilution directly affect measured values, or result in errors in a measurement of a biological component. If the doctor does not notice problems such as abnormal blood withdrawal during the monitoring, there is a probability that s/he regards the measured values with errors as accurate values and injects liquid medicines into the patient based on them.
In these situations are demanded biological component-measuring devices capable of continuously detecting changes in the dilution without imposing burden to patients, which enables the doctor to deal with problems such as abnormal blood withdrawal.
Patent document 1 discloses an automatic blood-pressure measuring device, though not a biological component-measuring device.
The automatic blood-pressure measuring device disclosed in Patent document 1 comprises a blood-pressure meter with a cuff wherein a blood pressure value of a living organism is measured by changing a squeezing pressure applied to a part of the living organism with the cuff, a hematocrit detector for continuously detecting a hematocrit value of the living organism, and a blood-pressure measurement actuator for automatically actuating the blood-pressure meter to measure a blood pressure of the living organism when a detected hematocrit value exceeds a preset reference value. See claim 1 of Patent document 1.
An example of the hematocrit detector included in the automatic blood-pressure measuring device of Patent document 1 is an optical noninvasive hematocrit sensor 72. Patent document 1 includes the following teaching about the optical noninvasive hematocrit sensor 72: “The sensor is equipped with a sensor clip 74 that includes a built-in light-emitting device for irradiating blood with a light beam having a predetermined wavelength, and a built-in light-detecting device for detecting light traveling through the blood and light scattered by the blood. The sensor clip 74 is fitted to a transparent container of the drip chamber 62 so that the container is held on with the sensor clip. The optical noninvasive hematocrit sensor calculates hematocrit values Ht in succession from the light detected by the light-detecting device, and continuously sends the calculated values to an inlet port 38 of the electronic controller 28. Because the hematocrit value Ht of a blood sample means a volume percent (%) of blood corpuscles in the sample, an increase in the hematocrit value means a decrease in the blood plasma whose percent by volume is obtained by subtracting the percent by volume of blood corpuscles from 100, represented by the equation (100−Ht) %.” See paragraph [0014] of Patent document 1.
Concerning the hematocrit value, Patent document 1 teaches the following: “The hematocrit value Ht of the blood of a dialysis patient, obtained from a signal outputted by a hematocrit sensor 72, is sent to the blood-pressure measurement actuator. Then, at step SA4 that corresponds to processing with the blood-pressure measurement actuator 84, the actuator judges whether or not the measured hematocrit value Ht is larger than a predetermined reference value A (%), or the percent by volume of the blood plasma of the dialysis patient is smaller than the criterion (100−A) %.” See paragraph [0022] of Patent document 1.
The teaching continues: “When the judgment at step SA4 is negative, the current routine is completed. On the other hand, when the judgment is positive, step SA5 and the following steps are carried out in the same way as the manual actuating operation explained above is carried out. As a result, a blood pressure measurement of the dialysis patient is automatically started, triggered by an increase in the hematocrit value Ht. See paragraph [0023] of Patent document 1.
The automatic blood-pressure measuring device disclosed in Patent document 1 boasts technical advantages thereof as follows: “As explained hereinbefore, the device of this working example has the blood-pressure measurement actuator 84 that enables the blood-pressure meter 80 to automatically start a blood-pressure measurement (at step SA9) when the actuator judges (at step SA4) that any one of the hematocrit values Ht continuously detected by the hematocrit sensor 72 exceeds a predetermined criterion A. In other words, the device of the invention is capable of measuring the blood-pressure value of a dialysis patient when the volume of the blood plasma circulating through the patient decreases, which enables the doctor to quickly provide the patient with medical treatment to deal with the blood pressure decrease.” See paragraph [0024] of Patent document 1.
Especially remarkable in the device disclosed in Patent document 1 are that the hematocrit sensor is a combination of the light-emitting device and the light-detecting device which are disposed so that they hold the drip chamber between them and that the percent by volume of blood corpuscles is obtained based on detection data outputted by the light-detecting device. Also, a decrease in the blood pressure of a patient during dialysis is predicted based on hematocrit values which represent the proportion (%) of the volume of blood corpuscles to that of the entire blood, and which values are measured by the optical method, in the invention disclosed in Patent document 1.
However, a prerequisite for measurement of the proportion of the volume of blood corpuscles to that of the blood with the automatic blood-pressure measuring device disclosed in Patent document 1, equipped with a combination of a light-detecting device and a light-emitting device is that blood withdrawn from a patient flows through an extracorporeal blood-circulating path 68. If the tip of an indwelling needle kept in a vein of a patient 58 is stopped up for some reason such as a contact of its opening end to the vascular wall, or a clog of blood adhering to the opening end of the indwelling needle or the inner wall of the circulating path therein, which results in prevention or blockage of the blood circulation, the blood of the patient 58 is not withdrawn properly though apparently blood is withdrawn from the patient 58 at a predetermined flow rate. Hematocrit values obtained in such a state do not represent accurate values of a dialysis patient, so that his/her blood pressure cannot be measured accurately. Another problem associated with this method is that measurement with a light-emitting device and a light-detecting device is prone to be affected by external disturbing factors such as variations in the temperature and incoming light beams, especially direct rays of the sun.    Patent document 1: JP H11-317 A (1999)